The objectives are to determine the intrinsic properties, and mode of synthesis and assembly of membrane proteins, and to apply these findings to the study of cell surfaces. Studies are in progress on the labeling of cell surface proteins with the lactoperoxidase-iodine technique, by examining the parameters determining the labeling of a single tyrosine residue with a known location on the inner surface of the outer membrane of E. coli. This residue is labeled from the outside in intact cells. Antibody prepared against purified nitrate reductase from E. coli will be used to study the synthesis and assembly of this membrane protein in both wild-type and mutant strains, and to study the mechanism by which a latent, membrane-bound protease converts this enzyme from a membrane-bound to a soluble form. We have found that the surface of E. coli cells undergoes extensive differentiation as a result of changes in growth rate or catabolite repression, and this is done by replacing outer membrane proteins with different polypeptides of the same molecular wieght. We will attempt to determine how these various polypeptides are regulated, and how they are modified and translocated from the cytoplasm to the outer membrane. Particular attention will be paid to the role of the attachment of sugars, lipids, or other substituents in the biosynthesis and translocation of these outer membrane polypeptides.